1. Field of the Invention
The present invention relates to apparatus for the distribution of particulate material onto a surface, in particular to an apparatus for the distribution of glass beads onto a line of paint and/or polymeric material previously applied to the surface of a road or the like, to produce retro-reflective traffic markings.
2. Description of the Related Art
In the application of traffic markings to road surfaces, it is generally desirable to apply a reflectorised material in the form of small glass spheres or beads to the marking for increasing night-time visibility and further extending the life of the marking. The glass beads may be applied with a paint binder in a single operation. An alternative method of application is to apply the paint binder separately from a paint application machine and then immediately follow the paint binder with an application of the glass beads from a distribution apparatus associated with the machine, from which the beads are dispensed by gravity flow.
It is important to dispense the glass beads at a uniform rate and evenly over the width of the marking, without spillage of the beads onto unwanted areas which can be both wasteful and may be damaging to the environment.
In U.S. Pat. No. 3,289,899 (Miller et al) there is described an apparatus for the distribution of glass beads onto a road surface in which the apparatus comprises a housing, an upper chamber within the housing for the receipt of glass beads, a lower chamber within the housing having a downwardly directed opening, and a distribution control valve positioned between the upper and lower chambers to allow the glass beads to pass in a controlled manner into a lower chamber, from where they fall through the downwardly directed opening onto the road surface. The distribution control valve is in the form of a conically-shaped spreader which is movable in a vertical direction from a position closing an opening between the upper and lower chambers to a position in which this opening is partially open. The glass beads then fall through an annular space between the surface of the spreader and the inside surface of the lower chamber and fall primarily in the form of a ring onto the road surface. The disadvantage of the apparatus described in U.S. Pat. No. 3,289,899 is that there is an accumulation of beads at the edges of the marking line and a shortage of beads at the centre of the marking line. Thus with this apparatus it is difficult to achieve uniform distribution of the beads on the road surface.
In European Patent EP129551-B (Road Construction Authority), there is described a glass bead applicator in which glass beads are stored in a pressurised hopper and fed to a nozzle from which they are projected, by means of compressed air, directly on to the road surface. This arrangement does not however result in a uniform distribution of the glass beads; there is a tendency for the beads to accumulate at the centre of the marking line. Further, the glass bead hopper must be pressurised and it is necessary to provide means for dehydrating the compressed air used to pressurise the hopper if one is to avoid condensation of moisture on the beads which could generate problems in their discharge from the nozzle.
It is an object of the present invention to provide an apparatus for sprinkling glass beads or other particulate material onto a surface, such as onto a line of freshly applied paint and/or polymer material applied to a road surface, in a manner which enables more uniform distribution to be achieved over a defined area in a simple and reliable manner.